This invention relates to a method of ore beneficiation.
The method is of particular value for concentrating sulphide ores which are finely distributed in shale or silica and is herein described in that context but is not limited to that use.
In outline, in traditional processes for concentrating sulphide ores, the ores are first crushed through primary jaw crushers and secondary cone crushers to yield a product 80% finer than about 3 mm. The crushed ore is then separated from low-grade material. Low-grade material is separated by a heavy medium process and the heavier high-grade ore is then ground to 90% passing 70-75 microns by means of rod or ball mills. The ball mill discharge is then subjected to further separation from gangue in flotation cells. In the case where lead and zinc sulphide ores are used, the lead ore is floated first and the slurry then conditioned, e.g. with copper sulphate, prior to the zinc being floated. The lead and zinc concentrates so obtained are subsequently de-watered and transported to smelters. This process and variations of it are well known in the art.
Up to a decade ago, flotation feeds were ground down to 75-100 microns. Over the past decade, a plant has been developed which enables flotation feeds to be ground to about 40 microns. That is achieved in tower mills having a nominal capacity in the range of from 10 to 100 tons per hour. A typical tower mill uses a screw agitator driven at 60 to 160 rpm and employs large balls (greater than 6 mm diameter) as a grinding medium. Although it has been claimed that tower mills may be effective with lead and zinc concentrates to reduce particles so that 80% are less than 10 microns, in practice tower mills cannot economically grind better than 80% less than 20 microns because of excessive energy, medium and wear costs.
There are many deposits (for example, those at the McArthur River in Australia) in which sulphide ores (for example, galena, pyrites) are finely distributed in a host gangue (for example, shale and/or silica) and which cannot be economically concentrated by known methods.